Explosive compositions containing guar gum derivative

ABSTRACT

A guar gum derivative comprising guar gum oxidized to a lower molecular weight is efficaciously employed as a cross-linkable thickening agent in explosive compositions, particularly explosive compositions including substantial amounts of a calcium-containing inorganic oxidizer, e.g., calcium nitrate.

United States Patent [191 Jessop 1 EXPLOSIVE COMPOSITIONS CONTAINING GUAR GUM DERIVATIVE [75] Inventor: Harvey A. Jessop, Murray, Utah [73] Assignee: Ireco Chemicals, Salt Lake City,

Utah

[22] Filed: May 14, 1973 [21] Appl. No.: 360,153

Related US. Application Data [63] Continuation of Ser; No. "197,373, Nov. 10, 1971,

[ June 17, 1975 [56] References Cited UNITED STATES PATENTS 3,617,401 11/1971 Mortensen et al 149/2 3,640,784 2/1972 Yancik et a1. 149/44 X 3,660,181 3/1972 Clay et a1 149/2 Primary Examiner-Leland A. Sebastian Attorney, Agent, or Firm-Merriam, Marshall, Shapiro & Klose {57] 7 ABSTRACT A guar gum derivative comprising guar gum oxidized to a lower molecular weight is efficaciously employed as a cross-linkable thickening agent in explosive compositions, particularly explosive compositions including substantial amounts of a calcium-containing inorganic oxidizer, e.g., calcium nitrate.

4 Claims, No Drawings EXPLOSIVE COMPOSITIONS CONTAINING GUAR GUM DERIVATIVE This is a continuation, application Ser. No. 197,373, filed Nov. 10, 1971; now abandoned.

The present invention relates to an improved method of thickening and cross-linking explosive compositions, and to the resulting explosive compositions. In general, it concerns the use of a guar gum derivative as an improved cross-linkable thickening agent in such compositions. More particularly, it involves explosive compositions containing a guar gum derivative consisting of a guar gum which has been oxidized to a lower molecular weight. Guar gum has for many years been commercially utilized in various explosive compositions. The ability of guar gum to fully hydrate in most concentrated salt solutions has encouraged its use in explosive compositions of the aqueous slurry blasting agent type, which employ inorganic oxidizer salt(s), such as ammonium nitrate (AN). In such prior art applications, guar gum is used as a thickening agent to increase the viscosity of the fluid ingredient(s) of the composition to the extent that solid particles present are suspended or dispersed and not permitted to segregate or settle. In many instances, care must be taken, however, to avoid increasing the viscosity to the extent that pumping of the ingredient becomes impractical, since pumping is commonly employed in either placing such compositions in boreholes or in packaging the compositions.

In many applications, explosive compositions containing a guar gum thickening agent are subjected to a cross-linking agent, to effect a cross-linking of the com position. As is well known in the art, borate ion, for example, can be used to cross-link guar gum containing explosive compositions. The advantages of a properly cross-linked composition, of course, primarily relate to its improved integrity or stability. In general, crosslinked aqueous slurry blasting agents are more resistent to deleterious environmental effects, such as leaching caused by water in the borehole. Moreover, an effective cross-link also helps to prevent coalescing of gas bubbles commonly present in aerated or otherwise gasified explosive compositions. In these latter type compositions, the gas bubbles help sensitize the composition by lowering the density and by providing hot spots or reaction sites upon compression by the detonation wave. The smaller and more evenly dispersed such bubbles are, the more sensitive the composition; so of course, coalescence is to be avoided and cross-linking is also used for that function. Proper requirement includes the requirment that the final cross-linking obtained be of satisfactory strength. In general, it is desirable to obtain as strong a final cross-link as possible. However, as is known in the prior art, the final crosslink strength of guar gum containing compositions is limited as a result of the very limited amount of guar gum which can be added without unduly increasing the viscosity of the composition to the point where it becomes unpumpable.

As mentioned above, care must be taken in formulating explosive compositions employing a cross-linkable guar gum to assure that the desired viscosity is attained, but not exceeded to the extent that pumping difficulties arise. In this regard, compositions containing substantial amounts of calcium ion present particular problems.

Calcium nitrate (CN) has recently come into substantial use in certain aqueous blasting agents. Commonly assigned copending application Ser. No. 148,941, filed June 1, 1971, now US. Pat. No. 3,787,254, for example, describes various explosive compositions containing CN.

Where CN-containing compositions are of interest, the present invention has particular utility or advantage.

In formulating aqueous blasting agents, it is common to employ one or more aqueous solutions of inorganic oxidizer salt(s). For example, AN-SN (sodium nitrate)-H O solutions have long been employed in the prior art. More recently, CN containing solutions such as CHANSN-H O solutions have been used to make explosive compositions having unique and useful characteristics. However, oxidizer solutions containing CN are considerably more difficult to thicken than those containing only monovalent cations. The reason for this is that the divalent calcium cations have the capacity to cross-link the guar gum generally used for thickeners; therefore, when the guar gum is introduced into the solution, the solvated calcium ions or complex calcium ions cross-link the gum, thereby blocking the entrance of water molecules (or other ions) which would otherwise cause the guar gum to hydrate and swell. However, such calcium cross-linking is migratory (in the pH range normally encountered, i.e., pH of about 3 to about 6) and thus hydration of the guar gum does eventually take place, but at a very slow rate depending upon such factors as pI-I, temperature, etc. Even under conditions conducive to hydration, it is a very slow process compared to the hydration of guar gum under the same conditions but in AN-SNH O solutions.

Moreover, when the guar gum has finally completely hydrated in a CN solution, it bears sufficient calcium cross-linking to render the solution (or suspension) considerably more viscous (and tacky) than would otherwise be the case in the absence of CN. The excessive viscosity of such solutions prevents using enough guar gum in the solution to achieve adequate initial and final strength and stability to the explosive composition when it is finally cross-linked. Thus, it is apparent that a problem heretofore has existed in formulating, with guar gum, properly thickened and cross-linked calcium containing aqueous blasting agents.

It has now been discovered that a guar gum derivative described hereafter, can be efficaciously employed as a cross-linkable thickening agent in explosive compositions. Briefly, the present invention is based, in part, upon the discovery that with such a guar gum derivative it is possible to obtain a final cross-link superior to that generally obtained with guar gum. In a preferred embodiment of the invention the guar gum derivative is employed in aqueous blasting agents containing substantial amounts of CN.

3 ing is accomplished through an alpha (l-6) linkage. The molecular weight of guar gum is about 220,000.

The guar gum derivative used in the present invention is prepared by oxidizing guar gum, thereby reducing the chain length of the guar gum molecule and also reducing its molecular weight. In the oxidation process, which may be a chemical oxidation or an enzymatic oxidation, it is believed that COOH and/or CHO groups are formed at the points where the chain is cleaved. Although the species or kind of functional group so formed can have some influence upon viscosity and/or cross-linking characteristics, any such effects are not believed to be of primary importance, in so far as the present invention is concerned. What is of primary importance about the oxidation process is that it results in a shorter chain length and lower molecular weight guar gum derivative. In comparison with guar gum, the guar gum derivative has a substantially shorter chain length; and, considerably greater amounts of the derivative can be used without adversely increasing the viscosity. Moreover, it has been discovered that the final cross-linking characteristics exhibited by a guar gum containing composition is primarily a function of the amount of guar gum or derivative present, and not its chain length. Thus, for example, because of the reduced chain length of the derivative it may be possible to use as much as four times more derivative to achieve a composition having a viscosity (at the time of pumping) comparable to a composition thickened with guar gum but the final cross-linking strength of the former composition is far superior to that of the latter.

The guar gum derivative will have a molecular weight substantially lower than the molecular weight generally accepted for guar gum, i.e., 220.000. In general, the guar gum derivative will have a molecular weight in the range of about 50,000 to about 150,000. A preferred guar gum derivative has a molecular weight of about 115,000. Guar gum derivative is commercially available at the present time from Stein, Hall & Co., Inc. under its designations L808 and 44-24", and from General Mills, Inc. under its designation 1 102.

The present invention will be further understood by reference to the following illustrative Examples. In the examples, unless otherwise indicated, all references to amounts or percentages are on a weight basis.

EXAMPLE I Number Average Composition Molecular Weight Guar Gum 218,300 Guar Gum Derivative (A) 1 14,400 Guar Gum Derivative (B) 105,000 Guar Gum Derivative (C) 62,400

EXAMPLE II In this example, tests were run to compare guar gum and guar gum derivative (A). In these tests CN- containing oxidizer solutions consisting of 25 parts AN,

20 parts CN, 3 parts SN, and 3 parts H O were thickened with either guar gum or guar gum derivative (A). 5 The 20 parts CN refers to 20 parts of Norsk Hydro calcium nitrate which is commercial grade CN consisting of about 80% calcium nitrate, about water (as water of crystallization) and about 5% ammonium nitrate.

Because of the lower molecular weight of the guar gum derivative (M =l 14,400), 4 times more (i.e., 0.4 part as compared to 0.1 part) of it was required in order to achieve a solution visocity equal to the solution viscosity attained with guar gum (M,,-=218,300).

Results of such tests showed that the guar gum derivative had a faster hydration time (about 30 minutes, versus about 2 hours for guar gum). In addition, the solution thickened with guar gum derivative was nontacky and did not otherwise exhibit any calcium ion induced cross-linking. In contrast, the solution thickened with guar gum was tacky and exhibited considerable calcium cross-linking.

EXAMPLE III In this example, two aqueous blasting agents or compositions were prepared using the thickened oxidizer solutions of Example II, and the cross-linked characteristics of the two resulting compositions were observed and compared. In these tests about 70 parts of each of the two different thickened oxidizer solutions of Exam ple II were separately used, with about parts of dry AN, 7.5 parts of fuel oil, and about 0.15 part of a crosslinking agent (consisting of 3 parts of water and 1 part Na Cr O '2H O).

The resulting composition which contained the guar gum was, after about 18 hours, still mushy and soft; while the resulting composition prepared from the guar gum derivative was much firmer and estimated to be about four times more water resistant. When a gassing agent such as sodium nitrite was included in such compositions, the resulting bubble structure of guar gum derivative containing compositions was superior to that of the guar gum containing composition in that the former compositions exhibited finer and more numerous bubbles than did the latter compositions.

EXAMPLE IV In this example, an explosive composition of the present invention and having the following composition was prepared and successfully detonated.

Composition Ingredients. (wt.7z)

Solution Containing:

AN CN (as in Example II) SN LII hard-solid -Contmued Composition 1% inches in length for 2" and 2%" dia. 24 inches in length for 4" dia.) at C. 2" diameter failed at 20C, 2%" diameter detonated at 5C, 2%" diameter detonated at 5C, 4" diameter detonated EXAMPLE V In this example, an explosive composition of the present invention was prepared.

Composition (wt/7r) Guar Gun derivative (A) Ethylene glycol Paint Grade Aluminum (Alcoa Gilsonite Brazilian Tapioca Flour Ground AN Crosslinking agent 1 part H Oll part Na Cr O .2H O) The composition of Example V can be packaged and used in small diameter blasting operations, for example as a replacement for dynamite. In such an application, the composition may be packaged in tubular polyethylene containers which have diameters in the range of about /8 of an inch to about 2 inches. Both ends of such tubular containers are then closed and secured, for example, by staples. The thus packaged explosive composition may then be loaded into the blasting site, which often consists of a long, horizontal, underground borehole. In such underground applications, it is common to encounter elevated temperatures in the range of, for example, 40C. The composition of the present invention offers a particular advantage in such applications since it remains firm even at such elevated temperatures. In contrast, prior art compositions necessarily containing lesser amounts of guar gum (instead of guar gum derivative) generally exhibits inferior properties at such elevated temperatures. Instead of remaining firm, such prior art compositions become loose, or limp, and thus more difficult to properly load.

As is apparent from the above examples, the guar gum derivative employed in the present invention offers several advantages over the prior art in formulating explosives compositions which utilize a cross-linkable guar gum thickening agent. Although the invention has particular advantage when used with CN containing compositions, its utility is not limited thereto but rather is also applicable to the formulation of any explosive composition in which a cross-linkable guar gum thickening agent has heretofore been used. Moreover, although the invention has been herein exemplified as utilizing a chromate ion cross-linking agent, equally satisfactory results are obtained when the cross-linking agent is of another type such as titanium ion, ferric ion, aluminum ion, borato ion and the like.

The relative amounts of the ingredients employed in the explosive compositions of the invention will, of

course, depend upon various factors such as the desired explosive strength, sensitivity, degree of cross-linking, and the like; and those skilled in the art will no doubt be able. by routine experimentation, to obtain desired optimum effects. Guar gum has been employed heretofore in small amounts, of less than about 1.0%, generally less than about 0.5% e.g., 0.271. As indicated above, greater amounts (at equivalent viscosity) of the guar gum derivative can be used due to its relatively low molecular weight; and, as a result, superior crosslinking characteristics can be obtained. Generally, such characteristics can be obtained by using less than about 1.0 weight guar gum derivative.

The explosive compositions of the present invention preferably are gasified by incorporation of small gas bubbles to a bulk density value less than the theoretical maximum density in order to thereby increase the sensitivity of the composition. Gasification techniques are well known in the art and any such technique can be employed to obtain a bulk density under service conditions regardless of the state of the composition of about 1.0 gms/cc or less to about 1.3 gms/cc, preferably about 1.2 gms/cc.

While the explosive compositions of the invention may, if desired, be used, i.e., detonated, immediately after being placed into a borehole, they also remain stable and thus may be detonated even after encoutering water in the borehole and/or being allowed to remain in the borehole for many days.

In addition to being used unpackaged, e.g., in large diameter borehole blasting operations, the compositions may also be packaged in any suitable container, for example, plastic bags or cardboard tubes and thereafter detonated in either vertical or horizontal boreholes, or any other desired location.

While the present invention has been described with reference to certain illustrative examples and preferred embodiments, various modifications will be apparent to those skilled in the art and any such modifications are intended to be within the scope of the invention as set forth in the appended claims.

What is claimed is:

l. A thickened, cross-linkable oxidizer saltcontaining explosive composition which is pumpable when initially formulated comprising an aqueous solution of at least one inorganic oxidizer salt; a guar gum derivative having a lower molecular weight than guar gum, contained and hydrated in said solution at time of formulation, in an amount sufficient to provide for strong, stable cross-linking of the composition, said derivative consisting essentially of guar gum which has been reduced to a molecular weight in the range of about 50,000 to about 150,000 prior to its addition to said composition; a cross-linking agent and a fuel.

2. A composition as defined by claim 1 wherein said inorganic oxidizer salt is calcium nitrate.

3. An explosive composition as defined by claim 1 comprising, by weight about parts of the oxidizer salt solution; about 0.55 parts of the guar gum derivative; about 20 parts dry ammonium nitrate; about 7.5 parts of fuel oil and about 0.15 part of a cross-linking agent.

4. A composition as defined by claim 1 wherein the molecular weight of the guar gum derivative is about 1 15,000.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO. 3,890,171 DATED June 17, 1975 |Nv ENTOR(S) Harvey A. Jessop It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 51, "requirement" should be cross-linking--; Column 2, line 15, "CH" should beCN-; Column 4, line 13,

"visocity" should be -viscosity; Column 5, line 2, move "dia." after -2 l/2-; Column 5, line 65, "borato" should be --borate; Column 6, line 27, "encoutering" should be encountering.

Signed and Scaled this A ttesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ommissinnvr oflarenls and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO. 3,890,171 DATED June '17, 1975 lN\/ ENTOR(S) Harvey A. Jessop It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Colunm 1, line 51, "requirement" should be -cross-linking-; Column 2, line 15, "CH" should beCN--; Column 4, line 13, "visocity" should be viscosity; Column 5, line 2, move "dia. after 2 l/2; Column 5, line 65, "borato" should be -borate-; Column 6, line 27, "encoutering" should be encountering.

Signed and Scaled this second Day Of March 1976 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner nj'Parenls and Trademarks 

1. A THICKENED, CROSS-LINKABLE OXIDIZER SALT-CONTAINING EXPLOSIVE COMPOSITION WHICH IS PUMPABLE WHEN INITIALLY FORMULATED COMPRISING AN AQUEOUS SOLUTION OF AT LEAST ONE INORGANIC OXIDIZER SALT, A GUAR GUM DERIVATIVE HAVING A LOWER MOLECULAR WEIGHT THAN GUAR GUM, CONTAINED AND HYDRATED IN SAID SOLUTION AT TIME OF FORMULATION, IN AN AMOUNT SUFFICIENT TO PROVIDE FOR STRONG, STABLE CROSS-LINKING OF THE COMPOSITION, SAID DERIVATIVE CONSISTING ESSENTIALLY OF GUAR GUM WHICH HAS BEEN REDUCED TO A MOLECULAR WEIGHT IN THE RANGE OF ABOUT 50,000 TO ABOUT 150,000 PRIOR TO ITS ADDITION TO SAID COMPOSITION, A CROSSLINKING AGENT AND A FUEL.
 2. A composition as defined by claim 1 wherein said inorganic oxidizer salt is calcium nitrate.
 3. An explosive composition as defined by claim 1 comprising, by weight about 70 parts of the oxidizer salt solution; about 0.55 parts of the guar gum derivative; about 20 parts dry ammonium nitrate; about 7.5 parts of fuel oil and about 0.15 part of a cross-linking agent.
 4. A composition as defined by claim 1 wherein the molecular weight of the guar gum derivative is about 115,000. 